President Obama makes his way to board Marine One from the South Lawn of the White House on March 23. / Mandel Ngan, AFP/Getty Images

by Janelle Dumalaon and Oren Dorell, Special for USA TODAY

by Janelle Dumalaon and Oren Dorell, Special for USA TODAY

BERLIN - President Obama and the leaders of the world's biggest economies met Monday to solidify their resolve to isolate Russia for its takeover of Crimea in a gathering to which Russian President Vladimir Putin was not invited.

The United States, Britain, Canada, France, Germany, Italy and Japan - collectively known as the Group of Seven - met on the sidelines of a scheduled nuclear summit in the Netherlands to discuss Crimea.

Russia usually joins such meetings of the group, which had been renamed the Group of Eight to reflects Moscow's participation.

"We're united in imposing a cost on Russia for its actions so far," Obama said after meeting with Dutch Prime Minister Mark Rutte.

In the interview with Dutch newspaper de Volkskrant , Obama conceded that the sanctions the U.S. and Europe imposed on Russia may not alter Moscow's stance in Ukraine, where people fear Putin may send his troops beyond Crimea into other parts of the country.

"If Russia continues to escalate the situation, we need to be prepared to impose a greater cost," Obama said.

The meeting at the Hague was previously scheduled to address nuclear terrorism, but Russia's military incursion into Ukraine would be a major source of discussion, said Obama's deputy national security adviser Ben Rhodes.

Obama's arrival in Europe came on a day when Ukraine's government ordered troops to pull back Monday from Crimea after Russian troops captured a third Ukrainian military base in the province of Crimea.

Putin annexed Crimea last week after Russian forces and pro-Moscow Crimean militiamen booted Ukrainian elected officials and held a referendum to secede. The West tarred the vote as illegal, and Ukraine said it was rigged to favor secessionists.

Kiev fears that Putin will now move to take over parts of East Ukraine on the pretext he used in Crimea that the area historically belonged to Russia and that ethnic Russians are in danger under the government in Kiev.

Russian Foreign Minister Sergey Lavrov met for the first time with his Ukrainian counterpart to discuss the situation after having said for weeks that Ukraine's government was illegitimate for having ousted pro-Moscow president Viktor Yanukovych.

Lavrov met with Ukrainian Foreign Minister Andriy Deshchytsia in the Hague, where both attended a summit on security.

Lavrov said Moscow was unconcerned by the snub of Putin. He said the meetings have been useful to discuss global crises but that Russia "will not be clinging to this format."

Obama told de Volkskrant that he does not want Europe to be viewed as a battleground between the East and West.

"That's the kind of thinking that should have ended with the Cold War," Obama said. "On the contrary, it's important that Ukraine have good relations with the United States, Russia, and Europe."

Analysts have said that the U.S. and EU have shown themselves to be relatively uniform in their efforts to bring Russia to heel.

"There has not been much difference between the details of the sanctions the U.S. and Europe have tried to mete out," said Wolfgang Richter, an senior associate at Berlin-based thinktank German Institute for International and Security affairs.

Europe has been cautious, critics say timid, about imposing harsh sanctions against Moscow because of the continent's economic relationship with the Russian government, especially when it comes to Russian natural gas.

"The U.S. is less dependent on mutual trade and gas imports from Russia," added Richter. "In addition, the U.S. only has an inter-agency process to cope with, Europe has 28 member states that have to agree."

Some analysts said fears that the two could be heading towards a new Cold War were misplaced.

"The Cold War analogy is a false analogy," said Judy Dempsey, the Berlin-based editor-in-chief of the Strategic Europe blog at think tank Carnegie Endowment for International Peace.

"The Soviet Union no longer exists, this is the Russian Federation we are dealing with. This is a strategy game in a globalized world, where Russian oligarchs also capitalize on globalization."

Btu Clifford Gaddy, a Russia scholar at the Brookings Institution, said the USA and its allies in Europe are in a new Cold War with Russia. He said it's unclear how much they'll be willing to fight it.

"We're talking about a very confrontationist relationship," said Gaddy, who co-authored a biography titled "Mr. Putin; Operative in the Kremlin."

"Putin is not going to back down on Crimea. It's more likely he moves ahead on other parts of Ukraine and probably elsewhere. We're not going to formally declare that we accept that."

The Ukrainian Defense Ministry said when Russian troops seized the marine base in the port of Feodosia - the tihird base to be taken - they detained up to 80 Ukrainian servicemen and took two injured Ukrainians away by helicopter.

Ukraine's Foreign Ministry said more Russian troops are coming into Crimea and large numbers of Russian forces bordering the mainland.

"The number of Russian armed forces on Crimean territory has risen to more than 22,000," Foreign Ministry spokesman Yevgeny Perebiynis told Interfax news agency.